Electronic trip units within circuit breakers for alternating and direct current distribution circuits are commonly used for protection against dangerous shocks due to line-to-ground current flow through the human body. These electronic trip units include, for example, ground fault circuit interrupters (GFCI) that sense a current imbalance between the phase and neutral conductors of the circuit breakers, arc fault interrupters, and overcurrent protection interrupters. The electronic trip units typically use a switching device to operate an actuator to trip or open the circuit to prevent a serious electrical shock or electrocution.
Electronic trip units may be tested to ensure proper operation, however, some failures of the switching device may occur that may render the circuit breaker inoperable without any indication. For example, an electronic trip unit may provide a trip signal to a switching device, for example, a transistor or SCR, which in turn energizes the actuator to cause the circuit breaker to trip. The circuit breaker circuitry is usually configured so that if the switching device fails shorted, the actuator is energized, the circuit breaker will trip, and the failure thereby detected. However, in this configuration, if the switching device fails open, the actuator cannot be energized, and the circuit breaker cannot be tripped automatically. Furthermore, if the actuator becomes electrically disconnected from the switching device, the actuator also cannot be energized and the circuit breaker cannot be automatically tripped. Presently, there are no techniques to detect this type of failure without removing the circuit breaker from service to be tested.
Accordingly, there is a need for automatically monitoring a circuit breaker to detect proper fault detection and to provide an indicator in the event of improper operation of the electronic fault protection.